This project involves studies of the expression of intracisternal A-type particles and a nucleoplasmic protein (termed germinal vesicle antigen) in preimplantation mouse embryos. Mouse genomic clones containing the genes for intracisternal A-type particles are being characterized with respect to cleavage pattern by restriction endonucleases, hybridization with labelled cDNA probes and by heteroduplex mapping. Segments of the A-particle genes will be labeled and used as probes in hybridization experiments to study the expression and properties of A-particle associated RNA in embryos. The amounts, synthesis and properties of the major A-particle structural protein and the germinal vesicle antigen will be studied by immunological methods such as radioimmunoassay and immunoprecipitation as well as by gel electrophoresis and cell fractionation.